The use of textile fabrics to form Strobel Insoles is known. The name “Strobel” was taken from the make of a German sewing machine that was originally used to produce shoes by a footwear construction method known as “California Slip Last”. Eventually, the terminology morphed into “Strobel Insole” or just “Insole”. In this regard, it is to be understood that the term “Strobel Insole” or “Insole” refers to the affixed insole of a shoe. This may be distinguished from the removable slip liner which is present in most athletic footwear.
The so called “California Slip Last” shoe construction became popular in the 1990s and has largely displaced the more traditional “Board Last” method, particularly in non-cleated athletic footwear. The process reduces material waste and is less capital intensive. In the “California Slip Last” process the Strobel Insole material is typically die-cut in the shape of the bottom of a person's foot. The shoe upper, which is typically fabric, is then sewn around the circumference of the Strobel Insole part to form a preliminary sock-like structure.
During the step of sewing the upper to the Strobel Insole, the sewing needle typically penetrates both the Strobel Insole and the upper material at approximately 2-3 mm from the edges of the materials to form the sock-like structure. Following the sewing step, the formed structure is then subjected to a so called “Lasting” process in which an insert called a “Last” resembling a foot is forced into the interior of the sock-like structure to establish a molded intermediate structure having the shape of a shoe. During the Lasting process, the Strobel Insole and the upper are subjected to substantial tensioning stress. The Strobel Insole material must have sufficient seam strength and low elongation properties under load in order to maintain consistent shoe size during the force of the Lasting process. After the Lasting process, glue is applied to the outside surface of the Strobel Insole and the midsole of the shoe is then adhered in underlying relation.
Stitch-bonding is a known process in which yarns are stitched through a substrate to form a coordinated web structure. By way of example only, and not limitation, exemplary stitch-bonding processes are disclosed in U.S. Pat. Nos. 6,855,392; 6,869,660; and 7,294,387 all of which are incorporated by reference as if fully set forth herein. In the past, Strobel Insole fabrics have been made by a stitch-bonding process utilizing a substrate of a carded and cross-lapped fleece containing a blend of polyester and bicomponent polyester fibers. The bicomponent fibers are typically a sheath/core configuration in which the core is made of PET polyester and the sheath is formed of lower melting point, co-polyester.
In accordance with the past practice, during the stitch-bonding process, the carded and cross-lapped fleece is stitched with polyester filament in closely spaced substantially parallel stitch lines in order to achieve strength, length direction stability and good seam holding properties. The resulting fabric is then heat set on a tenter frame. During heat setting, the sheath of the bicomponent fiber sheath melts and bonds to other fibers to provide dimensional stability in the cross machine direction of the fabric. Because this material is 100% polyester, the die-cutting waste can be collected, melted and extruded into polyester chip material. This polyester chip material can then be reprocessed back into polyester fiber and used again, This yields a closed-loop recycling process.
While the past formation practices have been highly functional, most current stitch-bonded fabric constructions used in Strobel Insoles are deemed to have a relatively rough surface feel. Recently, more attention has been given to the softness of the surface of the Strobel Insole surface inside the shoe. Although removable slip liners typically cover the Strobel Insole in the shoe, it has been found that in some instances it may be beneficial for the Strobel Insole itself to present a soft exterior surface. By way of example only, it is believed that such a soft exterior surface may be desirable to some users who remove the slip liner for insertion of an electronic device into a slot in the Strobel Insole for purposes of gathering performance data during use.
To reduce the surface roughness of the Strobel Insole, it is common for thin EVA foam materials to be laminated to Strobel Insole fabrics in order to provide a softer surface feel inside the shoe. However, a disadvantage of such foam lamination is that the die-cutting waste is no longer easily recyclable because the glue, fabric and foam are no longer compatible with each other in the recycling process. That is, the 100% polyester construction is sacrificed.
Accordingly a stitch-bonded Strobel Insole which provides reduced surface roughness while also being fully recyclable in a closed-loop system would be of substantial benefit.